Normal aging is often accompanied by a gradual decline in various physiological functions, which in some people results in physical impairments, and may lead to disabilities which worsen the quality of life and limit independence. Normal aging is also frequently associated with reduced circulating levels of GH, IGF-I, and sex steroids; decreased muscle mass and strength; and increased total and intra-abdominal fat. Treatment with recombinant human GH or sex steroids can improve body composition in some older persons, yet the effects of such hormonal treatment (singly or in combination) on various physiological functions remain to be defined. We hypothesized that age-related decreases in GH, IGF-I and sex steroids separately and interactively contribute to diminished skeletal muscle mass and strength, increased total and abdominal body fat, and reduced aerobic capacity in elderly women and men; and restitution of normal GH, IGF-I and sex steroid status by combined hormone therapy would exert additive or synergistic effects to increase muscle mass and strength, decrease total and intra-abdominal fat, and increase aerobic capacity.